1. Field of the Invention
The present invention is directed to a therapy system for treating a subject with focused acoustic waves, of the type having a source of focused acoustic waves, means for causing relative displacement of the focus zone of the focused acoustic waves and the subject to be treated, and a locating means for locating a region within the subject to be charged with the focused acoustic waves.
2. Description of the Prior Art
Therapy systems of the above general type, which advantageously operate non-invasively, are employed, for example, for the disintegration of calculi (lithotripsy), for the treatment of tumor pathologies (hyperthermia) or for treating bone conditions (osteorestoration). For implementing a therapy, the position of the region to be charged with the acoustic waves is first determined with the locating means. Subsequently, the focus zone of the acoustic waves and the subject to be treated are displaced relative to one another such that the focus zone coincides with the region to be charged with acoustic waves. This region is then charged with acoustic waves in the required way by the source of acoustic waves.
The problem arises in practice that the region to be charged with acoustic waves is not at rest, but exhibits a movement even given a sedate patient, this movement being caused, among other things, by the respiration of the patient. According to a method disclosed by German Patent 31 46 628, in order to improve the "on target" reliability, the emission of shockwaves is only allowed to ensue in such a phase of the respiratory cycle wherein the region to be charged with acoustic waves moves little. Another improvement of the "on target" reliability can be achieved when, according to European Application 0 244 730, a chronological correlation of the operation of the locating means such as an x-ray system, and the output of the acoustic waves is additionally produced. Because, however, the movement of the region to be charged with the acoustic waves is subject to certain irregularities, an adequately high "on target" reliability can not be achieved under all circumstances even with this latter method. This also true of a therapy apparatus disclosed by German OS 39 00 893 wherein the overlap between a calculus to be disintegrated and the focal zone is calculated and is displayed as a function of time, so that the operating personnel have additional information available.
Moreover, German OS 40 34 533 discloses the use of an ultrasound locating means, operating according to the echo locating principle.
A therapy system disclosed by European Application 0 168 559 also offers an improvement in the targeting reliability, by using two locating devices spatially correlated to one another, either both operating on an ultrasound basis or one operating on an ultrasound basis and the other operating on an x-ray basis. Since only two slices of the patient can be scanned in the case of two locating means operating on an ultrasound basis, the position of the region can no longer be identified as soon as the region to be charged with the acoustic waves moves out of one of the two slices. This is similarly true for the combined x-ray and ultrasound locating. Although the region will usually be visible in the x-ray image, the region will repeatedly enter and leave the slice scanned with the ultrasound. The result is that the spatial position of the region cannot be identified. Again, therefore, the "on target" reliability is in need of improvement.